In general, in order to improve thermal stability and surface gloss of ABS copolymer resins or similar resins, an amount of thermal stabilizer added is increased or remaining monomers are removed by stripping ABS copolymer latexes, or water is further added during aggregation and dehydration to minimize a residual emulsifier content.
In addition, in order to improve impact resistance and falling ball impact resistance, generally, content of a rubber component is increased or an acrylonitrile content is increased during production of ABS copolymers. When the content of rubber component is increased, impact resistance and whiteness are improved, but, disadvantageously, molecular weight and graft ratio of resins are decreased and colorability is thus deteriorated. Furthermore, when the acrylonitrile content is increased, impact resistance and colorability are excellent, but resin whiteness is disadvantageously decreased.
In addition, a rubber-reinforced resin such as acrylonitrile-butadiene-styrene (ABS), methacrylate-butadiene-styrene (MBS) or acrylonitrile-styrene-acrylate (ASA) is generally produced by preparing a rubber-reinforced resin through emulsion polymerization, aggregating and drying the resin to obtain a powder, and primarily processing the powder with a resin such as styrene-acrylonitrile (hereinafter also referred to as “SAN”) or polycarbonate (PC) into a pellet in an extruder. A moisture content of the rubber-reinforced resin added to the extruder used is generally 1% or less. In some cases, the primary processing may be carried out by a continuous process wherein a powder having a moisture content of about 30% after dehydration is mixed with SAN and PC in the extruder without the drying process. In this case, high moisture content causes problems such as variation in physical properties and deterioration in production efficiency.
Accordingly, an important factor in maintaining production efficiency and quality upon addition of a powder containing moisture to an extruder without a drying process is minimization of moisture content. A conventional centrifugal dehydrator is limited in terms in ability thereof to reduce moisture content.
This problem may be overcome by using a squeezing dehydrator. However, it should be considered that this squeezing dehydration may cause problems such as deterioration in thermal stability and deformation of resins because it entails a high-temperature and high-pressure process.